Abstract
IN a paper read on November 13 to the Students' Section of the Institution of Electrical Engineers, Mr. H. M. Wells discusses the effects of the rapid increase of the telephone service in Great Britain on the methods of working. The country is divided up into zone areas and subdivided into group areas. Major trunk lines connect main zone exchanges with London and with one another. They are so designed that a minimum of duplicate plant is necessary. By the use of thermionic amplifiers, the volume of speech fed into a line is made equal to the volume received at the far end. When things are properly adjusted, there is thus no loss of sound. One result is that the speech on the London-Moscow circuit is as good as that on a local London call. The insulation materials of the cables used are paper and ‘air-space’. The ‘air-space’ is filled with carbon dioxide which possesses desiccating qualities and can be readily pumped out from the cable and replaced by fresh gas capable of restoring the dry atmosphere required to maintain a high insulation resistance. In the exchange itself, the type of apparatus employed is designed to permit calls to be completed on demand, that is, whilst the calling subscriber is held on the line. Timing the duration of calls is a problem which has received special attention. In the trunk exchanges, all calls are timed automatically; this obviates any error due to the human element, and, as the calls are expensive, this is very desirable. The particulars from the time-recording instruments, together with the called and calling subscribers' numbers, are entered on a ticket by the operator and circulated to a central pricing position. The circulation is effected by pneumatic tubes. The power for the exchange is derived from secondary cells of large capacity. A voltage of 50 is used for normal speech and apparatus purposes, but the signalling lamps on the switchboard are worked at six volts from an alternating current source.
Article PDF
Rights and permissions
About this article
Cite this article
The London Telephone Trunk Exchange. Nature 138, 1006–1007 (1936). https://doi.org/10.1038/1381006c0
Published:
Issue Date:
DOI: https://doi.org/10.1038/1381006c0